I'd probably use a menu slide. If you "daisy chain" presentations like that by linking from the last slide of presentation 1 to the first slide of presentation 2, you'll eventually end up with all 25 presentations open.
If you're presenting with the PPT Viewer -- say on a CD or something -- it will play all the presentations in order if you specify that in the Viewer settings when you do the Package for CD process. But if you're using PowerPoint itself, I think you'd have to jump through some hoops to get it to use a playlist.